Interfacing spontaneous breathing and mechanical ventilation. New insights.
Mechanical ventilation (MV) with positive pressure insufflations of gas into the lung may be required to ensure sufficient oxygenation of blood and elimination of carbon dioxide in acute respiratory failure. Interfacing spontaneous breathing and mechanical ventilation has been used to improve gas exchange and may offer other advantages regarding integrity of lung tissue. Airway pressure release ventilation (APRV), or bilevel positive airway pressure (BiPAP), is a mechanical ventilatory mode with a low respiratory rate upon which spontaneous breaths can be superimposed during any time of the respiratory cycle. The mechanical pressure variations cause inflation and deflation of the lungs and the spontaneous breaths are added according to the demand of the respiratory center and neuromuscular function. This technique improves oxygenation of blood compared to MV alone. This seems to be caused by recruitment of collapsed lung tissue and increased aeration of the lung. Moreover, ventilation is distributed more to the dependent (dorsal in supine position) regions than with mechanical ventilation alone. Since blood flow goes preferentially to the dependent regions, the altered ventilation distribution results in improved matching of ventilation and perfusion, further enhancing or facilitating gas exchange. Moreover, there is less cyclic collapse, i.e. less re-collapse during expiration and reopening during inspiration than with MV alone. Further development of the interfacing technique can be expected, with synchronization and also dosing of the mechanical support and with triggering of the ventilator that is based on neural recordings rather than mechanical signals as pressure and flow.